Power tools may be of different types depending on the type of output provided by the power tool. For example, a power tool may be a drill, hammer, grinder, impact wrench, circular saw, reciprocating saw, and so on. Some power tools may be powered by an alternating current (AC) power source while others may be portable and may be powered by a direct current (DC) power source such as a battery pack. In power tools using a brushless DC (BLDC) motor, a series of electronic switches are used to electronically energize motor windings sequentially in order to drive the motor rotor. Using these switches, the speed and rotational direction of the rotor can be controlled.
The switching operation of the electronic switches results in a significant amount of heat. In many power tools, airflow channels are provided to carry heat away from the switches. Heat sinks are also typically provided adjacent the switches for heat dissipation. The heat sinks and air channels are often sized and designed suitable to the power tool's normal usage. However, extraordinary conditions may result in unusual heating of the power switches. It is thus desirable to provide a cost-effective design to safeguard against the power switches overheating when such conditions occur.